1. Field of the Invention
The present application relates generally to throttle loss recovery systems for internal combustion engines, and relates more particularly to a butterfly bypass valve useful in such systems as well as in other applications.
2. Description of Related Art
The power output of spark ignition engines, as well as some diesel engines, generally is controlled by a throttle plate or butterfly valve whose position is governed by the setting of the accelerator pedal or the like. As the throttle plate is moved to narrow the flow passage for the intake air, the air flow rate is reduced, which reduces the torque and power output from the engine, and correspondingly the air is expanded (i.e., loses pressure) before reaching the engine intake manifold. This throttling of the intake air causes a loss in overall engine efficiency because in effect the engine must work harder to pull the air through the restricted throttle.
Thus, throttle loss recovery (TLR) systems, typically turbine-generator systems, have been developed that seek to regulate the flow of intake air while recovering some of the energy lost in the throttling process. During at least some engine operating conditions, the air destined for the engine intake manifold first passes through a turbine that expands the air and drives an electrical generator. Thus, the turbine acts as the throttle during such conditions. However, these prior systems have often failed to satisfactorily address the issue of controllability, specifically, how to ensure that the total air flow rate into the intake manifold responds to the driver's demanded power (i.e., accelerator pedal position) in an appropriate way.